Plant functional constraints on foliar N:P ratios in a tropical forest landscape

Although large scale analyses of foliar N:P ratios suggest and overall pattern of P limitation in tropical forests, analyses within the biome are less indicative of a consistent pattern of nutrient limitation. High tree species diversity and soil heterogeneity are important factors driving the variability of foliar chemistry in the tropics; however, this variability could be reduced at the level of the functional characteristics of the species present at a site. In this study it is hypothesized that foliar N:P ratios would be more constrained when the species are grouped according to functional characteristics, and would reveal patterns of nutrient limitation. The study was conducted in a tropical forest landscape of the Porce region in Colombia, which consists of patches of primary and secondary forests of different ages. The functional groupings revealed consistent patterns of conservative N cycling in species present at young secondary sites, as well as conservative P cycling of the species present later in succession and in primary forests. Although the observed data have limitations in terms of capturing the overall variability for each functional group, the classification used here provided support for the proposed hypotheses. It is concluded that functional composition, rather than taxonomic composition, can potentially improve our understanding of nutrient cycling in tropical forests

Effects of processes at the population and community level on carbon dynamics of an ecosystem model

Ecological processes at the population and community level are often ignored in biogeochemical models, however, the effects of excluding these processes at the ecosystem level is uncertain. In this study we analyzed the set of behaviors that emerge after introducing population and community processes into an ecosystem carbon model. We used STANDCARB, a hybrid model that incorporates population, community, and ecosystem processes to predict carbon dynamics over time. Our simulations showed that at the population level, colonization and mortality rates can limit the maximum biomass achieved during a successional sequence. Specifically, colonization rates control temporal lags in the initiation of carbon accumulation, and mortality rates can have important effects on annual variation in live biomass. At the community level, differences in species traits and changes in species composition over time introduced significant changes in carbon dynamics. Species with different set of parameters, such as growth and mortality rates, introduce patterns of carbon accumulation that could not be reproduced using a single species with the average of parameters of multiple species or by simulating the most abundant species (strategies commonly employed in terrestrial biogeochemical models). We conclude that omitting population and community processes from biogeochemical models introduces an important source of uncertainty that can impose important limitations for predictions of future carbon balances

The climate benefit of sequestration in soils for warming mitigation

Soils are an enticing reservoir for nature-based climate solutions, but long timescales are required to store amounts of C of relevance to mitigate warming acknowledging its impermanence. Scientific clarity on the controlling factors in soil C persistence should help to disambiguate debates related to permanence in the climate policy domain. However, another contributing factor that is lacking in this debate is a way to compute the climate benefits of C in terrestrial ecosystems over time in the same units as greenhouse gas emissions. We use a case study approach here to demonstrate the use of the metrics of carbon sequestration (CS) and climate benefit of sequestration (CBS) with the aim of assessing the contribution of simultaneous emissions and uptake on radiative forcing. We show how this new computational framework quantifies the climate benefit achieved in two different agricultural systems, one a managed tropical perennial grass system in HawaiModified Letter Turned Commai, USA and the other a boreal (cold-temperate, semi-humid) agricultural soil from long term amendment trials in Sweden. Using a set of computations, we show how C inputs and persistence interact to produce different levels of radiative forcing at relevant time frames, which could greatly help to clarify issues of carbon permanence discussed in climate policy. Temporary soil C storage could help to decrease peak warming provided that ambitious emission reductions are part of the portfolio of solutions; the CS and CBS framework gives us a way to quantify it based on biogeochemical understanding of soil C persistence

Information content and maximum entropy of compartmental systems in equilibrium

Although compartmental dynamical systems are used in many different areas of science, model selection based on the maximum entropy principle (MaxEnt) is challenging because of the lack of methods for quantifying the entropy for this type of systems. Here, we take advantage of the interpretation of compartmental systems as continuous-time Markov chains to obtain entropy measures that quantify model information content. In particular, we quantify the uncertainty of a single particle's path as it travels through the system as described by path entropy and entropy rates. Path entropy measures the uncertainty of the entire path of a traveling particle from its entry into the system until its exit, whereas entropy rates measure the average uncertainty of the instantaneous future of a particle while it is in the system. We derive explicit formulas for these two types of entropy for compartmental systems in equilibrium based on Shannon information entropy and show how they can be used to solve equifinality problems in the process of model selection by means of MaxEnt.Comment: Code repository: https://github.com/goujou/entropy_and_complexity_in_e

Aridec: an open database of litter mass loss from aridlands worldwide with recommendations on suitable model applications

Plant litter decomposition in terrestrial ecosystems involves the physical and chemical breakdown of organic matter. Development of databases is a promising tool for achieving a predictive understanding of organic matter degradation at regional and global scales. In this paper, we present aridec, a comprehensive open database containing litter mass loss data from aridlands across the world. We describe in detail the structure of the database and discuss general patterns in the data. Then, we explore what are the most appropriate model structures to integrate with data on litter decomposition from the database by conducting a collinearity analysis. The database includes 184 entries from aridlands across the world, representing a wide range of climates. For the majority of the data gathered in aridec, it is possible to fit models of litter decomposition that consider initial organic matter as a homogenous reservoir (one pool models), as well as models with two distinct types of organic compounds that decompose at different speeds (two pool models). Moreover, these two carbon pools can either decompose without interaction (parallel models) or with matter transfer from a labile pool to a slowly decomposing pool after transformation (series models). Although most entries in the database can be used to fit these models, we suggest that potential users of this database test identifiability for each individual case as well as the number of degrees of freedom. Other model applications that are not discussed in this publication might also be suitable for use with this database. Lastly, we give some recommendations for future decomposition studies to be potentially added to this database. The extent of the information included in aridec in addition to its open-science approach makes it a great platform for future collaborative efforts in the field of aridland biogeochemistry

Ideas and perspectives: Allocation of carbon from net primary production in models is inconsistent with observations of the age of respired carbon

Carbon allocation in vegetation is an important process in the terrestrial carbon cycle; it determines the fate of photoassimilates, and it has an impact on the time carbon spends in the terrestrial biosphere. Although previous studies have highlighted important conceptual issues in the definition and metrics used to assess carbon allocation, very little emphasis has been placed on the distinction between the allocation of carbon from gross primary production (GPP) and the allocation from net primary production (NPP). An important number of simulation models and conceptual frameworks are based on the concept that C is allocated from NPP, which implies that C is respired immediately after photosynthetic assimilation However, empirical work that estimates the age of respired CO2 from vegetation tissue (foliage, stems, roots) shows that it may take from years to decades to respire previously produced photosynthates. The transit time distribution of carbon in vegetation and ecosystems, a metric that provides an estimate of the age of respired carbon, indicates that vegetation pools respire carbon of a wide range of ages, on timescales that are in conflict with the assumption that autotrophic respiration only consumes recently fixed carbon. In this contribution, we attempt to provide compelling evidence based on recent research on the age of respired carbon and the theory of timescales of carbon in ecosystems, with the aim to promote a change in the predominant paradigm implemented in ecosystem models where carbon allocation is based on NPP. In addition, we highlight some implications for understanding and modeling carbon dynamics in terrestrial ecosystems

Carbon translocation from glacial and terrestrial to aqueous systems – characteristics and processing of dissolved organic matter in the endorheic Tibetan Lake Nam Co watershed

The Tibetan Plateau (TP) comprises sensitive alpine environments such as grassland biomes. Climatic changes and intensifying land use threaten these ecosystems. Therefore, it is important to understand the response of ecosystems to changing biotic and abiotic factors. The translocation of dissolved organic matter from glacial and terrestrial to aqueous systems is an important aspect of this response, specifically when characterizing changing conditions of freshwater resources and sensitive limnic ecosystems on the TP. Via changes in its chemical composition, characteristics, transformation and processing of DOM can be tracked. Three catchments of the Nam Co watershed of the TP (Niyaqu, Qugaqie and Zhagu) and the lake were investigated to understand how site specific terrestrial processes and seasonality affect the composition of DOM and alteration of organic compounds in streams and the lake of this endorheic basin. Four hypotheses were tested: H1 The natural diversity in the Nam Co watershed controls site specific effects on DOM composition. H2 Seasonal effects on DOM composition are driven by warm and moist summers influenced from the Indian summer monsoon (ISM) and cold and dry winters. H3/ H4a Site specific effects on DOM diminish by means of biological decomposition and photooxidation of DOM during the stream path / in the lake. Alongside H4b organic matter of the Nam Co Lake is independent from catchment influences, given by an autochthonous source of DOM. A multi-parameter approach was applied, consitsing of water chemistry parameters (pH, electric conductivity, cations and anions, dissolved inorganic carbon), concentration of dissolved organic carbon (DOC), DOM characteristics (chromophoric DOM, fluorescence DOM and δ13C of DOM) and DOM ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Sampling was conducted for three seasons, freshet in 2018, the phase of the ISM in 2019 and post-ISM baseflow in 2019. Alongside a watershed-wide plant cover estimate was composed, to explore the link between differences in DOM characteristics and degree of green plant cover. Sampling covers stream water, as well as endmember samples such as: glacial effluents, water of springs and water from an alpine wetland. The lake was covered by sampling the brackish zone and the lake pelagial and the lake surface. The composition of DOM differed between the three endmember groups and between stream samples of catchments. Glaciers showed a dual DOM source, indicating a glacial microbiome and compounds derived from burned fossil fuels. Springs differed based on their geographic location. Upland waters showed limited inputs of alpine pastures: lowland springs displayed influences of yak faeces with microbial reworked DOM, indicated by less negative δ13C and nitrogen. Wetlands were distinguished by more eutrophic conditions by highest concentrations in DOC and high amounts in N-heteroatoms. Streams were site specific with input sources derived from glaciers, wetlands, groundwater, intense animal husbandry and a plant-derived phenolic signature from alpine pastures aligned to the degree of plant cover. Seasonality affected DOM characteristics in stream water. During freshet, DOM was plant-derived, as was during baseflow conditions. A flush of dissolved organic carbon, accompanied by a compositional shift towards more microbial derived DOM was observed during the ISM season. Processing of DOM in streams was limited to the biolabile fraction of DOM of the glacial biome. Transformation of DOM was overruled by the constant input of plant derived phenolic DOM compounds from alpine pastures. Consequentially, the brackish intermixing zone showed the inflow of terrestrial DOM into the lake. In contrast, lake water exhibited distinct DOM characteristics, by lowest amounts in aromatic molecular compounds and DOM rich in 13C. This suggested intense processing of phenolic, terrestrial derived DOM by photooxidation, as well as a seasonally stable autochthonous DOM source derived from algae and microorganisms in lake water. In conclusion, DOM characteristics are largely influenced by local endmembers such as glaciers, springs and wetlands. Seasonality shows that shifts in the onset, and changes in the intensity of the ISM can largely modify DOM composition. Processing of DOM took place mainly in the lake. The study revealed that DOM is suited to function as a monitoring agent in this lake watershed. Hence, DOM is a helpful tool to understand changes in ecosystems, and forthcoming, to safeguard sensitive ecosystems of the TP.Deutsche Forschungsgemeinschaft (DFG)/International Research Training Group (GRK 2309/1)/317513741/E

Barcelona SMARTMOTO CHALLENGE

In this paper we present the rules of the first edition of the SMARTMOTO CHALLENGE, www.smartmotochallenge.org . It will take place during the 2012-2013 season, showing the vehicles in July 2013 at the ParcMotor of Igualada and in Barcelona City. This is a competition of an electric motorcycle development where students, from participating universities, must make an electric motorcycle in accordance with the rules that we expose here. Following the successful example in the automotive industry with the Formula SAE, started in the USA, and now in full expansion in Europe with the Formula Student, we want to launch an Spanish but international competition oriented to the light electrical bikes.Postprint (published version

Cronología de inundaciones y sequías en el noreste de la provincia de Buenos Aires 1911 - 1989

p.241-249El objetivo del presente trabajo consistió en reproducir, por medio del balance hídrico del suelo, la cronología de inundaciones y sequías del Noreste de la Provincia de Buenos Aires y evaluar si la misma pudo darse dentro de un régimen de lluvias completamente aleatorio o si requirió que el mismo contuviera componentes determinísticas, como ciclos, periodicidades o saltos climáticos para producirse. Muchas de las series de datos mensuales empleadas presentaron una leve tendencia positiva, aunque en ningún caso resultó significativa debido a la alta variabilidad natural del fenómeno, que también puede ser interpretado como un salto de los promedios 1971-89 con respecto a los 1911-70, dado que tomados aisladamente ninguno de los dos períodos presenta tendencia. El análisis espectral reveló algunos picos levemente significativos y cuasi significativos, pero con una contribución muy pequeña a la variancia total, lo que hace descartar los efectos de procesos periódicos o cuasi periódicos. El estudio de rachas reveló que las de precipitación son completamente aleatorias y ráramente exceden los tres meses de duración, mientras que las de humedad del suelo muestran un proceso markoviano con alta persistencia pudiendo llegar a los 18 meses de extensión. Comparado con el período 1911 -70, el período 1971 -89 presentó un predominio de las rachas húmedas

Modelo local de simulación de nivel de napa freática en la Depresión del Salado

p.155-158A partir del esquema clásico del balance hidrológico seriado se elaboró un modelo que estima la variación mensual del nivel de napa freática a partir de las características físicas del suelo y de la precipitación y la evapotranspiración potencial mensuales. El modelo se ajustó tomando como referencia las series mensuales de las localidades de Dolores (1942-1977) y Chascomús (1945-1951). Pudo comprobarse que, tomando como partida los datos observados, el modelo reproduce ajustadamente el comportamiento de la napa durante 7 años, apartándose luego gradualmente. Por lo que posee capacidad para interpolar largos períodos faltantes en las series de observaciones, problema que se presenta frecuentemente con los registros de napa freática. El estudio se realizó para localidades situadas en la Depresión del Salado, lo que determina que el modelo sea de validez local ya que no se consideró el aporte de agua desde otras localidades debido a la escasa pendiente de la zona y a las características de drenaje de los suelos, las cuales determinan un movimiento vertical lento del agua debido a la presencia de horizontes de escasa permeabilidad